Abstract
The lifetime of the second 2 + state in 94 Zr was redetermined by the Doppler- shift attenuation method following inelastic neutron scattering (DSAM-INS) from metal- lic Zr and ZrO2 samples of natural isotopic abundance. The new value for the level lifetime differs significantly from the previously published value, with the new lifetime found to be roughly twice that value. A reanalysis of the original -ray data from the enriched 94 ZrO2 sample failed to expose the source of this discrepancy; however, powder X-ray diffraction and scanning electron microscopy performed on each scattering sam- ple, including the enriched sample used previously, provide clues to an explanation and reveal the role of the chemical properties of the sample material in DSAM-INS lifetime determinations.
Highlights
Several years ago, our group performed 94Zr(n, n′γ) measurements with an enriched 94ZrO2 scattering sample
Based on the observation that the 752-keV transition from the second 2+ state at 1671 keV to the first excited state at 919 keV exhibits a large B(M1; 2+2 → 2+1 ), we identified the second 2+ state as the lowest mixed-symmetry state [1, 2]
As questions have recently been raised about this anomaly, we carried out additional (n, n′γ) measurements using metallic zirconium, zirconium (IV) oxide, and zirconium (IV) hydroxide samples of natural isotopic composition
Summary
Our group performed 94Zr(n, n′γ) measurements with an enriched 94ZrO2 scattering sample. Based on the observation that the 752-keV transition from the second 2+ state at 1671 keV to the first excited state at 919 keV exhibits a large B(M1; 2+2 → 2+1 ), we identified the second 2+ state as the lowest mixed-symmetry state [1, 2] These measurements of 94Zr revealed anomalous behavior not observed in any other nucleus; the B(E2) value for the transition from the second excited 2+ state to the ground state was found to be larger than that from the first 2+ state to the ground state. This nucleus emerged as the lone example of an inversion of the E2 strengths for the lowest-lying 2+ excitations. As questions have recently been raised about this anomaly, we carried out additional (n, n′γ) measurements using metallic zirconium, zirconium (IV) oxide, and zirconium (IV) hydroxide samples of natural isotopic composition
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